The invention arose in the design of a craft of the type in which a fan is used to direct a radial jet of air over a curved canopy. The canopy is shaped so as to divert the flow of air from a radial to an axial direction to produce lift. This invention deals with the problem of increasing lift.
It is known, eg from U.S. Pat. No. 5,203,521 that, in vehicles of this type, the turning of the fan also tends to produce an unwanted turning of the canopy. U.S. Pat. No. 5,203,521 relates to an aircraft having an upper deflector which deflects air from a fan onto an annular body. The deflector is supported onto the annular body by spacers or struts which form spoilers designed to give air from the fan a circumferential component of motion to counteract the spin cause by the propeller. Because U.S. Pat. No. 5,203,521 assumes that the air from the fan follows in a radial direction, the spoilers or struts have upstream portions which are angled, if away from the radial, in a direction opposite the direction of flow.
In U.S. Pat. No. 5,803,199 the unwanted turning is counteracted using trimming vanes located on the lift generating surface of the canopy.
More recently, as described in WO/2006/100526 , it has been recognised that the air flowing from the fan tends to follow, depending on its velocity, a complex swirling trajectory over the canopy surface rather than a direct path in a vertical axial plane WO/2006/100526 describes a technique by which this phenomenon, in conjunction with fins on the canopy, can be used to prevent the abovementioned counter spin.